Structures of photoactive proteins studied by (in-situ) neutron scattering
Project: Structures of photoactive proteins studied by (in-situ) neutron scattering
Countries and institutions involved in the project:
Institute of Physics, University of Tartu,
Prof. Jörg Pieper, pieper [ät] ut.ee
Institute of Biology, Humboldt Universität zu Berlin
Prof. Athina Zouni, athina.zouni [ät] hu-berlin.de
Institut für Chemie, Technische Universität Berlin
Prof. Thomas Friedrich, friedrich [ät] chem.tu-berlin.de
Project objectives: A proper understanding of protein function requires detailed knowledge about protein structure, which will be demonstrated for two attractive examples. First, photosystem I (PSI) is a remarkably stable membrane protein converting solar energy into electrical and finally storable chemical energy. PSI is of great biotechnological interest as it can be integrated into biohybrid photoelectrochemical cells. For electrode design, structural characterization of the complex formation between PSI and electron donors/acceptors like cytochrome c6, ferredoxin and FNR is needed. Second, the orange carotenoid protein (OCP) is photoswitchable and undergoes a structural transition to its active state upon illumination. Despite of many efforts, the active state structure is still elusive. In the absence of high-resolution structures for the latter examples, small angle neutron scattering (SANS) is the technique of choice to investigate structures in aqueous solution, complex formation or light-induced structural changes. Since PSI is a membrane protein, SANS studies require solubilization using deuterated detergents, which are “invisible” with proper contrast matching and do thus not affect the structure determination of the PSI complexes. In contrast, SANS studies of OCP require the design of a setup for in-situ illumination during the SANS experiments. Both applications will deliver unique structural information.
Countries and places where the project will be carried out: The Institute of Physics, Tartu, Estonia, is responsible for preparing and performing the neutron scattering experiments (small angle scattering) and for construction of a setup for in-situ optical excitation of the samples. Finally, data analysis and the development of structural models will be carried out here.
The Humboldt Universität zu Berlin, Germany, will prepare and supply complexes of PSI with different electron donors and acceptors for biotechnological applications. In this regard, it is absolutely essential for the success of the SANS experiments that PSI will be isolated using fully deuterated (“invisible”) detergents for SANS with contrast variation, because matching of protonated detergent is inherently incomplete and may result in artifacts in structural models derived from SANS data.
The group at Technische Universität Berlin, Germany, will prepare samples of the orange carotenoid protein with different carotenoid content and complexes with fluorescence recovery protein using partial deuteration for SANS with contrast variation.
The experiments will be carried out at MLZ Garching, Germany, using small angle neutron scattering, in part with in-situ illumination, within the user service of the neutron scattering facility. One scientist of the Tartu group has to travel to Garching to carry out this experiment.
Public events within the project: Workshop „Biophysical applications of neutron scattering techniques“.
Direct and indirect target group of the project: Estonian and Baltic neutron scattering community, international biophysics and neutron scattering community.